The CPT is the most sensitive measure available of sustained attention in preschool and school age children. Reaction time and number of errors differentiate normal groups of children from those with Attention Deficit Hyperactivity Disorder (ADHD). Recent studies of developmental aspects of sustained attention have shown that the CPT can be used effectively in 4- to 7-year old children. The Phase I research will yield a greatly improved, system independent, CPT software instrument to measure attention in 4- to 7-year old children. Phase II will produce a standardized, sophisticated CPT available for different platforms (Macintosh System 7.x; Motorola 68K/Power PCS; PC Intel MS NT). The use of highly sophisticated computer technologies within this simple to operate CPT instrument will: (1) empower much larger numbers of users in children hospitals, day care centers, preschools and/or children homes;; (2) enable better standardized measurement of attention in preschool children, and early diagnosis and treatment of ADHD; and (3) allow easy data sharing and analysis within the educational/medical/ scientific research community. This new valid CPT can be used for a wide variety of screening, diagnostic, prognostic, scientific and educational purposes.